hw # 5 /tutorial # 5 wrf chapter 19; wwwr chapter 20 id ... · , flows through a 2.5 cm diameter...
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HW # 5 /Tutorial # 5
WRF Chapter 19; WWWR Chapter 20
ID Chapters 7-9
• Tutorial # 5
• WRF#19.3; WRF#19.8; WWWR #20.13,; WRF#19.23, WWWR#20.42.
• To be discussed during the week 15 Feb. – 19 Feb., 2021.
• By either volunteer or class list.
• Homework # 5 (Self practice).
• WRF#19.4; WRF#19.24; WRF#19.25
• ID# 7.24, 7.35.
• Correction: #20.42: Table: Unit for Cp should be corrected from J/kg-K to kJ/kg-K.
Convective Heat Transfer
Correlations
Natural Convection
Horizontal Plates
McAdam’s Correlations: Hot surface facing up or cold surface surfacing down
H
C
H
C
Horizontal Cylinders
g
In each of the correlations to follow the temperature of the hotter of
the two large surfaces is designed in T1, and the cooler surface is at
temperature T2.
Fluid properties are evaluated at the film temperature,
Tf = (T1 + T2) / 2.
Convective heat flux is expressed as
q
A= h(T1 - T2)
Example 1
H
H
Initial Guess T = 385K, Resulting T=381.1K Second Iteration
Forced Convection For Internal
Flow
Turbulent Flow
Example 2
Hydraulic fluid (MIL-M-5606), in fully developed flow
, flows through a 2.5 cm diameter copper tube that is 0.61m long,
with a mean velocity of 0.05 m/s. The oil enters at 295K. Steam
condenses on the outside tube surface with an effective heat transfer
coefficient of 11400 W/m2-K. Find the rate of heat transfer to
the oil.
Ro
RiRc
Rc << Ro, Ri295K
Example 2
Ro
Ri
=(295+305)/2
Rc
Rc << Ro, Ri295K
305K?
=373-(373-300)*[98.1/(98.1+11400)]
=372.3K
Example 3
Forced Convection For External
FlowFlow Parallel To Plane Surface
Cylinders In Crossflow
Tube Banks In Crossflow
SL : Center-to-center distance between tubes along the direction of flow
ST: Center-to-center distance between tubes normal to the direction of flow
Adapted from ID Page 437